The tourism industry is notoriously vulnerable to the ups and downs of the U.S. economy, but this year a host of factors have combined to form a magic mix that promises the best summer season in years in Central Florida.

The decline of the U.S. dollar in relation to European currencies got 1986 off to a quick start. Even tourism from Latin America, which has been weak since 1982, shows promise of roaring back, experts said.

Domestic tourism got a boost from dropping gasoline prices and air fares, along with a generally favorable U.S. economy.

Then, in April, acts of terrorism abroad dealt a severe blow to international travel by Americans. Some travel agents have reported cancellation rates of up to 80 percent by Americans who had planned to vacation in Europe.

All this translates into lots and lots of tourists coming to Central Florida, which usually gets from 8.5 million to 10 million visitors a year.

''We're having a great, great year,'' said Janeen Dunbar, a spokeswoman for Wet 'n Wild, an Orlando water park. The park does not release attendance figures, but Dunbar said it is beating projections that were set above last year's record level.

''All indications are that it will be a very strong summer,'' Disney World spokesman Charles Ridgway said.

Sea World's attendance is up 9 percent through April compared with the first four months of last year, which itself was a record year, said Sea World of Florida president Bob Gault. At Cypress Gardens in Winter Haven, attendance year-to-date is 35 percent ahead of last year.

''Summer is looking great,'' agreed Bob Stolz, vice president of SKF Group, which owns the Buena Vista Palace and the Hotel Royal Plaza on Disney property at Lake Buena Vista.

Last year this time, Stolz said, reservations for July at the Buena Vista Palace hotel showed a 31 percent occupancy level. This year, July is already 78 percent booked. This year there are twice as many rooms reserved for June and August as there were at this time last year.

Disney-owned hotels, Ridgway said, ''are very heavily booked'' for June, July and August, even though Disney has added 500 rooms in the past year.

Stolz said terrorism is the primary reason for the increased bookings at the Buena Vista Palace.

State Farm Insurance Cos. cancelled trips to Vienna, Austria, and Lisbon, Portgual, for its top agents because of a fear of reprisals by terrorists. Instead, State Farm has booked 15,000 room-nights at the Buena Vista Palace and the Hilton hotels at Lake Buena Vista in July and August, Stolz said.

Using the average rate of $96 a room as computed by Laventhol & Horwath for Lake Buena Vista hotels, the 15,000 room-nights mean $1.44 million in room revenue alone.

Pat Yelvington, president of the Central Florida Hotel-Motel Association, said room rates in past years have risen steadily. This summer, though, rates at many hotels are holding steady, mostly because of a 60 percent increase in the number of rooms since late 1982, she said.

Clyde Rodgers, a partner at Pannell Kerr Forster, an accounting and consulting firm, said occupancy levels at area hotels will be in the low 80s in June, the mid-80s in July and in the mid- to upper-70s in August.

Another problem faced last year -- a severe shortage of qualified workers -- may be less severe this summer.

Lester Gibb, a counselor-interviewer at the Job Service of Florida, a state agency that helps businesses find qualified workers, said the worker shortage has eased a bit because salaries have been raised.

Hotels, attractions and fast-food restaurants ''found out they had to pay more'' to attract workers, Gibb said. Starting pay for entry-level jobs at tourism-related businesses is usually $3.75 to $4 an hour, he said.

Patsy Harris, program director for the Mayor's Youth Employment Program in Orlando, said the program's sign-up rate -- both by businesses and job seekers -- is running ahead of last year's level.

About 113 companies have listed jobs with the program, and 200 students aged 16 to 21 have signed up. Many of the jobs are tourism related, she said. Attractions, too, are aggressively courting workers.

Disney has done some recruiting at local colleges and made plans for some workers to move from one department to another in times of severe shortages, Ridgway said.

Disney will hire from 1,500 to 1,700 full- and part-time workers for the summer season, said spokesman Bob Mervine.

Gault, of Sea World of Florida, said he is optimistic the park can get the workers it needs, having embarked on an aggressive hiring program to get them. On Friday and Saturday, Sea World enticed workers to apply by promising applicants two free tickets to the park.Sea World will have about 1,050 jobs available this summer, including 800 slots for summer seasonal workers and about 250 permanent positions, according to spokeswoman Holly Eby.

Tourists from Latin America could further swell crowds in Central Florida this summer because several South American economies are staging strong comebacks, according to wholesale tour operators.

Favorable exchange rates, enabling Europeans in particular to travel to the United States less expensively than last year, have led the U.S. Tour and Travel Administration to predict a 10 percent increase in the number of foreign visitors in 1986.

Frank Bastidas president of Americana Tours Inc. in Miami, a tour wholesaler whose company does 90 percent of its business with Latin Americans, said bookings have jumped 50 percent this summer compared with the year before.

This is good news for Central Florida, because ''our best destination is Orlando,'' Bastidas said.

''They come to Miami to go shopping, but most of their time is spent in Orlando because of its attractions,'' Bastidas said.